Variable polarity pulse with constant droplet size

ABSTRACT

An electric arc welder including a high speed switching power supply with a controller for creating high frequency current pulses with negative polarity components through the gap between a workpiece and a welding wire advancing toward the workpiece. Molten metal droplets are quickly created during negative polarity portions of the weld cycle. Welding controls include integrating a parameter during the negative polarity portions to determine when a desired amount of energy has been generated at the welding wire. This energy is associated with a desired droplet size for consistent droplet transfers to the workpiece.

The present invention relates to the art of electric arc welding using agas metal arc welding (GMAW) process and more particularly to a GMAWelectric arc welder that creates a high frequency chain of pulses toform a series of weld cycles constituting a weld process.

INCORPORATION BY REFERENCE

The following patents include information related to the subject matterof the current application and are also incorporated by reference hereinin full: U.S. Ser. No. 13/293,103, filed Nov. 9, 2011; U.S. Ser. No.13/293,112, filed Nov. 9, 2011; U.S. Ser. No. 13/543,545, filed Jul. 6,2012; U.S. Ser. No. 13/554,744, filed Jul. 20, 2012; U.S. Ser. No.13/625,188, filed Sep. 24, 2012; and U.S. Ser. No. 13/788,486, filedMar. 7, 2013.

BACKGROUND OF THE INVENTION

In electric arc welding, a popular welding process is pulse welding,which primarily uses a solid wire electrode with an outer shielding gas.Gas metal arc welding (GMAW), such as metal inert gas (MIG) welding,uses spaced pulses which first melt the end of an advancing wireelectrode and then propel the molten metal from the end of the wirethrough the arc to the workpiece. A globular mass of molten metal ordroplet is transferred during each pulse period of the pulse weldingprocess.

SUMMARY OF INVENTION

Alternating current (AC) welding can include negative current during anegative polarity portion in the pulse waveform. The negative polarityportion can build a molten droplet on the end of the wire very quicklyand can be difficult to control. Because adaptive control methodstypically look at the long term running average of the waveform,regardless of the polarity, the size of any particular droplet can varyfrom cycle to cycle. The pulse peaks following the formation of thedroplets must be large enough to transfer the largest possible dropletexpected, even if the actual droplet is smaller. This condition canresult in inconsistent droplet transfers, for example, with spattering,poor appearance, and excessive heat.

In one embodiment, an electric arc welder includes a high speedswitching power supply with a controller for creating high frequencypulses through a gap between a workpiece and a welding wire advancingtoward the workpiece, a wave shape generator to define a shape of thehigh frequency pulses and a polarity of the high frequency pulses, andwherein the wave shape generator senses feedback from an arc through thegap and ends a negative polarity portion when a function of the feedbackreaches a predetermined value.

The descriptions of the invention do not limit the words used in theclaims in any way or the scope of the claims or invention. The wordsused in the claims have all of their full ordinary meanings

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings, which are incorporated in and constitute apart of the specification, embodiments of the invention are illustrated,which, together with a general description of the invention given above,and the detailed description given below, serve to exemplify embodimentsof this invention.

FIG. 1 is an exemplary combined block diagram and system architecturefor an exemplary welder for performing an embodiment of the presentinvention;

FIG. 2 is an exemplary circuit diagram of an exemplary motor controllerin an embodiment of the present invention;

FIG. 3A is an exemplary circuit diagram of an exemplary variablepolarity switch in an embodiment of the present invention;

FIG. 3B is another exemplary circuit diagram of another exemplaryvariable polarity switch in an embodiment of the present invention;

FIG. 4 is a drawing of exemplary welding arcs showing positive andnegative polarity effects;

FIG. 5 is an exemplary current graph illustrating the high frequencypulses and negative polarity components along with exemplary dropletstates;

FIG. 6 is an exemplary power graph and current graph illustrating thehigh frequency pulses and negative polarity components;

FIG. 7 is an exemplary current graph illustrating exemplary features ofthe high frequency pulses and negative polarity components used in anembodiment of the present invention;

FIG. 8 is an exemplary logic diagram and flow chart to obtain exemplaryhigh frequency pulses with exemplary features, including negativepolarity components;

FIG. 9 is an exemplary logic diagram and flow chart to determine the endof an exemplary negative polarity component;

FIG. 10 is another exemplary logic diagram and flow chart to determinethe end of an exemplary negative polarity component;

FIG. 11 is another exemplary combined block diagram and systemarchitecture for an exemplary welder for performing an embodiment of thepresent invention;

FIG. 12 is an exemplary block diagram showing an exemplary waveincorporating an exemplary workpoint;

FIG. 13 is an exemplary look up table including workpoints;

FIG. 14 is an exemplary waveform graph illustrating an exemplary shortcircuit and a subsequent negative polarity component; and

FIG. 15 is another exemplary waveform graph illustrating anotherexemplary short circuit and another subsequent negative polaritycomponent.

DETAILED DESCRIPTION

Referring now to the drawings, which are for the purpose of illustratingexemplary embodiments of the invention only and not for the purpose oflimiting same, FIG. 1 discloses an exemplary welder A having a generallystandard configuration, including a high speed switching power supply10, such as an inverter or buck converter, with an input rectifier 12and an output transformer 14 directing current pulses by way of avariable polarity switch 16 to an electrode E. In this embodiment, thepower supply regulates the current of the pulses. However, in otherembodiments, voltage or combinations of voltage and current may beregulated to define the high frequency pulses. An exemplary variablepolarity switch 16 is described in more detail below in association withFIG. 3A. The electrode E includes a wire 20, such as an aluminum wire,from a spool or drum 22 and advanced by feeder 30 toward workpiece Wthrough the action of motor 32. Motor 32 is controlled with a motorcontroller 31. An exemplary motor controller is shown in FIG. 2, where apulse width modulator 34 controls the speed of motor 32 and thus feeder30 under direction of a feedback tachometer 36 and an operationalamplifier 40 for comparing input 42 from tachometer 36 with a commandwire feed speed (WFS) signal in the form of a level on line 44. Othermotor controllers 31 may also be used.

Referring back to FIG. 1, as the aluminum electrode or wire E advancestoward workpiece W, an arc is created across gap g by a series ofcurrent pulses, which may include pulse peaks, a background current, anda negative polarity current.

Referring now to the exemplary power supply, the inverter stage includesa switching type inverter 10 provided with power from a three phasevoltage source L1-L3 having a frequency of 50 or 60 Hz according to thelocal line frequency. The AC input voltage is rectified by rectifier 12to provide a DC link 11 directed to the input of inverter 10. Theoutput, or load of inverter 10 is transformer 14 having a primarywinding 15 a and secondary winding 15 b with a center tap 17 connectedto the workpiece W. Secondary winding 15 b is directed to the variablepolarity switch 16 to create output lines 24, 26 connected to electrodeE and workpiece W.

The variable polarity switch 16 can be any switching device capable ofswitching polarity signals on output lines 24, 26, such as thosedescribed in U.S. Ser. No. 13/788,486, which is incorporated byreference herein in full. For example, FIG. 3A shows an exemplaryvariable polarity switch 16 with a positive rectifier circuit 28 havingdiodes D1, D2, D3 and D4 to create a positive output terminal 38 and anegative output terminal 46 connected to an output switching network 48.Output switching network 48 may include two transistor type switches SW1and SW2, usually in the form of insulated-gate bipolar transistors(IGBTs) that can be turned on and off according to the logic on baselines 55, 56. To dissipate high voltages when switches SW1, SW2 are off,snubber networks 57, 58 are connected across the switches SW1, SW2.Other configurations of switching networks, such as, for example,switching network 48′, as shown in FIG. 3B, and discussed below, mayalso be used. Network 48 can be used for pulsating high welding currentssubstantially over 200 amperes. A single output inductor 72 is dividedinto positive pulse section 74 and negative pulse section 76. In thismanner, an AC current is created in output lines 24, 26 connected toelectrode E and workpiece W. By alternating the logic on base controllines 55, 56 in succession, a high frequency alternating current isapplied to the welding circuit including electrode E and workpiece W.The AC frequency is determined by the frequency at which the logicalternates on base control lines 55, 56. The logic on these lines may begenerated by a software program or subroutine processed by amicroprocessor in, for example, a wave shape generator or wave shaper80, described in more detail below.

FIG. 3B shows another exemplary variable polarity switch 16′ using afull wave bridge. Output switching network 48′ may include fourtransistor type switches SW1, SW2, SW3, and SW4, that can be turned onand off according to the logic on base lines 55, 56. When SW1 and SW2are on, the electrode E is positive; when SW3 and SW4 are on, theelectrode E is negative. Network 48′ can also be used for pulsating highwelding currents substantially over 200 amperes. In this manner, an ACcurrent is created in output lines 24, 26 connected to electrode E andworkpiece W. By alternating the logic on base control lines 55, 56 insuccession, a high frequency alternating current is applied to thewelding circuit including electrode E and workpiece W. The AC frequencyis determined by the frequency at which the logic alternates on basecontrol lines 55, 56. The logic on these lines may be generated by asoftware program or subroutine processed by a microprocessor in, forexample, a wave shape generator or wave shaper 80, described in moredetail below.

Referring back to FIG. 1, arc current is read by sensor 52 to create avoltage signal in line 52 a representing arc current I_(a). In a likemanner, arc voltage is sensed by sensor 54 to create a voltage signal online 54 a representing arc voltage V_(a). In accordance with standardpractice, processing devices, such as those represented as controller 60and wave shaper or generator 80, are connected to power supply 10 tocreate pulses in accordance with the feedback current I_(a) and/orvoltage V_(a). For example, controller 60 may include a pulse widthmodulator driven by an oscillator having a frequency exceeding 100 kHz.The pulse width modulator can produce a current pulse during each outputof the oscillator. The pulse width determines the amplitude of thecurrent pulse. The level of current during the welding cycle includesmany pulses from the pulse width modulator.

As so far described, exemplary welder A is a welder with controller 60and wave shaper 80 controlling the wave shape of the current pulses andwave shaper 80 and variable polarity switch 16 controlling switching andpolarity, which both contribute to defining the welding cycle at gap g,which creates the welding arc. The controller 60 receives a commandsignal on line 70 from the wave shaper 80. The voltage on line 70determines the profile, shape, and/or contour of the current pulses ofthe welding process. This configuration has been popularized by, forexample, the Power Wave brand of welders from The Lincoln ElectricCompany, and in particular, for example, the Power Wave S350, S500,R350, R500, Super Glaze, Super Arc, and Blue Max.

In accordance with the invention, wave shaper 80 controls the signal online 70 to shape the high frequency pulses used in the welding process.Control logic 90, as shown in FIG. 8 and described in more detail below,repeatedly initiates logic, software, or a routine to create repeatingweld cycles. In some embodiments, the wave shaper 80 may include thecontrol logic 90, and any other logic that creates the desired waveform.As described above, to create the high frequency alternating currentapplied to the welding circuit across the electrode E and workpiece W,the wave shaper 80 controls the logic on control lines 55, 56 to createalternating polarity currents. Also, as mentioned above, in variousembodiments, the high frequency pulses may be regulated by current,voltage, or combinations of voltage and current, including non-linearcombinations.

Changing the polarity of portions of the pulses, between positive andnegative, can allow for greater control of the heat created duringwelding. The arcs created by positive and negative polarity currentsexhibit several differences during welding because the behaviors andcharacteristics of the cathode and the anode are not the same. Inparticular, during welding, the heat generated at the cathode and theheat generated at the anode are significantly different. When thepolarity of the current is reversed (e.g., switched from positive tonegative or from negative to positive), the anode and cathode areexchanged, which causes the heating characteristics of these regions toreverse.

FIG. 4 is a drawing of exemplary welding arcs that highlights some ofthe differences between exemplary arcs during positive and negativepolarity portions of the welding waveform or pulse wave. In general,although welding always adds heat to the workpiece W, negative polarityportions of the weld cycle add less heat to the puddle of the workpieceW than positive polarity portions. During a positive polarity portion,an arc 111 spreads across a puddle 112, heating up a wide area. On thepositive electrode E side, the arc 111 is concentrated at the bottom ofdroplet 113. The current flows through the droplet 113 and itsassociated magnetic pinch force acts on the liquid droplet 113, thuseventually pulling it from the electrode E to the workpiece W. However,during a negative polarity portion, an arc 115 is concentrated on thecenter of a puddle 116, allowing the edges to cool off and start tosolidify. On the negative electrode E side, the arc 115 covers much moreof the end of the electrode E, heating up a large molten metal droplet117. In this manner, much of the current does not flow through thedroplet 117, and its associated pinch force is not applied to the liquiddroplet 117, so it hangs at the end of the electrode E, getting bigger.This large liquid droplet 117 is transferred to the workpiece W with thenext positive polarity pulse peak.

Negative polarity increases the burn-off rate of the electrode E as heatis built up in the electrode E, which also allows the weld puddle tocool off. Therefore, when the current has a positive polarity, most ofthe heat is dissipated or absorbed into the weld puddle of the workpieceW. When the current has a negative polarity, more of the heat isdissipated or absorbed into the electrode E, with much less heatdissipated into the weld puddle of the workpiece W.

FIG. 5 depicts an exemplary pulse wave PW in accordance with anexemplary embodiment of the present invention. In particular, FIG. 5shows a simplified welding waveform or pulse wave PW with a negativepolarity component 120, along with drawings of the various stages ofelectrode E droplet formation and deposition onto workpiece W, labeledas roman numerals I-VI. FIG. 5 shows a complete welding cycle of a pulsewave PW, where the waveform cycle has a peak pulse portion 122, anegative polarity portion 120, and a background portion 124. In theembodiment shown, the peak pulse portion 122 is the portion of thewaveform cycle having the maximum current level for the pulse wave PWcycle, and typically represents the droplet transfer portion of thepulse wave PW. In typical pulse welding waveforms, a peak portion 122and a background portion 124 may be combined such that a waveformalternates only between peak pulse portions 122 and background portions124. In such embodiments, the background portion 124 is used to beginthe melting of the electrode E to form a molten droplet, prior to thepeak portion 122. In these embodiments, the end of the electrode Estarts to form a relatively small droplet. A small amount of initialmelting can be disadvantageous in some welding applications.Furthermore, an increase of current in the end of electrode E (toincrease melting) before the peak pulse portion 122 may not be desirablebecause of the additional energy and heat ultimately input into theworkpiece W during this process. Thus, embodiments of the presentinvention employ current pulse waves PW that have a negative polarityportion 120, for example, between the peak pulse portion 122 and thebackground portion 124. For simplicity, the embodiments shown in thedrawings utilize current regulation, including for defining the negativepolarity portion 120, peak pulse portion 122, and the background portion124. In other embodiments, the pulse PW can also be regulated withvoltage, or combinations of voltage and current to define the portionsof the pulse wave PW, including, for example, the negative polarityportion 120, peak pulse portion 122, and the background portion 124.

As shown in FIG. 5, an exemplary pulse wave PW includes a negativepolarity portion 120 after the peak pulse portion 122. As shown at I,because the flow of current is in the opposite (negative) direction, thearc A has a different shape or profile than during the other polarity(positive). Specifically, as mentioned above in relation to FIG. 4, witha negative polarity, the current creates an arc A which envelopes moreof the electrode E, rather than being focused out of the end of theelectrode E. By extending the arc A up the electrode E, more surfacearea of the electrode E is heated and thus more heat is input into theelectrode E, without increasing the current. Because of this, themelting of the end of the electrode E is increased and a much largermolten droplet D is created at the end of the electrode E, as shown atII. Further, this larger droplet D is created: 1) without an increase inenergy usage by the welding power supply; and 2) with less heattransferred into the workpiece W. As shown at III and IV, following thenegative polarity portion 120, the background portion 124 isimplemented, followed by the peak pulse portion 122. The affect of thecomplete pulse peak portion 122, effectively transferring droplet D toworkpiece W, is shown in roman numerals IV through VI, after which thenegative polarity portion 120 is repeated. Roman numerals IV and Vdepict the pinch force acting on the electrode E during transfer of thedroplet D to the workpiece W. Embodiments employing a pulse wave PW witha negative polarity portion 120 are able to decrease the amount ofenergy needed to transfer a droplet D, increase the amount of consumablewire transferred per pulse cycle from the electrode E, and/or decreasethe amount of heat transferred to the workpiece W.

In other embodiments, the sequence of the various portions of the pulsewave PW may be different. For example, the background portion 124 mayprecede the negative polarity portion 120. Further, it is noted that insome exemplary embodiments of the present invention, it is not necessaryfor the negative polarity portion 120 to be timed immediately after thepeak pulse portion 122 or immediately before the background portion 124,but an intermittent current portion can be inserted in between theseportions. In these embodiments, this intermediate current portion may beat the current level of the background portion 124 and may have arelatively short duration. In other embodiments, the current level atthis intermediate portion may be lower than the background portion 124to allow for better switching of the polarity of the current. Theduration of the intermediate portion could be any duration that does notinterfere with the creation and transfer of the droplet D to theworkpiece W.

FIG. 5 shows an embodiment of the present invention where the magnitudeof the current during the negative polarity portion 120 has the samemagnitude as the background portion 124, but has an opposite polarity.However, in other exemplary embodiments of the present invention, thecurrent during the negative polarity portion 120 can have a magnitudewhich is different than that of the background portion 124.

In addition, the exemplary pulse wave PW shown in FIG. 5 is shown withnegative polarity portions 120 having the same duration T. The negativepolarity portion 120 can build the droplet D on the end of the electrodeE very quickly. Inconsistent durations T could result in inconsistentdroplet D sizes because more or less time would allow more or lessenergy to be absorbed by the electrode E, which directly impacts thesize of the droplet D formed and the ability of the pulse peak 122 totransfer that droplet D. More energy absorbed by the electrode E duringa negative polarity portion 120 would result in a larger droplet D.

Although not shown in FIG. 5, variations in arc length or voltage canalso affect the amount of energy absorbed by the electrode E during anegative polarity portion 120. Even if the magnitude of the current andthe duration T during the negative polarity portion 120 are maintained,variations in voltage will result in droplet D size variation. Inparticular, an increase in the arc length or gap g will result in anincrease in voltage to maintain the current through the arc. Like anincrease in duration T, an increase in voltage during the negativepolarity portion 120 results in more energy absorbed by the electrode Eand a larger droplet D. The peak pulse portions 122 following theformation of the droplets D must be large enough to transfer the largestpossible droplet D expected, even if the actual droplet is smaller.Inconsistent droplet D sizes results in inconsistent droplet transfersbecause the peak pulse portion 122 is not optimized for transferringdroplets of different sizes. Adaptive control methods are inadequate toadjust for these conditions because they typically look at the long termrunning average of the waveform and the size of any particular droplet Dcan vary from cycle to cycle.

It has been determined that the size of a droplet D is directlyproportional to the energy absorbed by the electrode E during thenegative polarity portion 120. Based on feedback from or about the arcat the gap g, the amount of energy absorbed during the negative polarityportion 120 can be determined by calculating the integral of powerduring the negative polarity portion 120 as follows:∫[power during portion 120]=∫[(current during portion 120)*(voltageduring portion 120)]

In reference to the welder of FIG. 1, for example, for feedback aboutthe arc at the gap g, the measurements I_(a) and V_(a) (via signals 52a, 54 a) are available to the wave shaper 80:∫[power during portion 120]=∫[I _(a) *V _(a) during portion 120]

Calculating the integral of power during the negative polarity portion120 allows the welder, e.g., via the wave shaper 80, to reliably controlthe size of the droplet D formed during the negative polarity portion120 of the pulse wave PW, including during variations in arc length orvoltage. In particular, the negative polarity portion 120 of FIG. 5 withduration T may be replaced with a control system that ends the negativepolarity portion when the desired energy has been absorbed by theelectrode E, as determined by the integral of power during the negativepolarity portion.

FIG. 6 shows a current-regulated embodiment and an exemplary power graphalong with an associated exemplary current graph of pulse wave PW′. Asmentioned above, in other embodiments, voltage or combinations ofvoltage and current may also be regulated to define a pulse wave. Thegraph of power includes a lower voltage portion and a higher voltageportion, which may be caused by, for example, variations in arc lengthor gap g. As shown in FIG. 6, negative power portions 130, 132 havedifferent magnitudes 140, 142, respectively. In particular, negativepower portion 130 is associated with a relatively lower voltage and hasa lower power magnitude 140. In contrast, negative power portion 132 isassociated with a relatively higher voltage and has a higher powermagnitude 142. Because the power has a greater magnitude during thehigher voltage portion, a droplet D on electrode E would form faster byabsorbing energy faster during the higher voltage portion.

By integrating power during the negative polarity portion of thewaveform, energy absorption of the electrode E and droplet D can bedetermined and managed. To ensure that droplet D sizes are maintained ata desired size or “set point”, even during variations in voltage,negative polarity portions can be stopped when a desired energy level orjoule level, for example, as measured by integrating power, has beenreached. For example, negative polarity portions associated with highervoltages (e.g., 132) are ended sooner than negative polarity portionsassociated with lower voltages (e.g., 130). Referring to FIG. 6:

X=power in watts (I_(a)*V_(a));

∫X=total energy in watt*seconds or joules; and

Y=desired energy in joules that correlates to the desired droplet Dsize.

As shown in FIG. 6, the actual energy level ∫X reaches the desiredenergy level Y after different durations of negative polarity portions160, 162 due to the differences in voltage during these portions. When∫X reaches the desired energy level Y, the negative polarity portion ofthe pulse wave PW′ is stopped at 150 after duration 160 during the lowervoltage portion and at 152 after duration 162 for the higher voltageportion. Thus, the droplets D formed on the electrode E during the lowerand higher voltage portions will be the same size. In this manner, thenegative polarity portion of the pulse wave PW′ is stopped when thedroplet D has reached the desired size, regardless of voltage (andcurrent) variations.

In other embodiments, a voltage calculation may also be used todetermine when the droplet D has reached the desired size. For example,the integral of voltage may be used when the current is known.

In exemplary embodiments of the present invention, the duration of thenegative polarity portion can range from, for example, 100microseconds-20 milliseconds. In other exemplary embodiments, thenegative polarity portion has a duration which is in the range of, forexample, 0.3% to 50% of the welding cycle.

The pulse wave PW′ current graph shown in FIG. 7 is an exemplaryembodiment achieved by having wave shaper 80 control the welding cyclewith current regulation. The particular shape of the pulse wave PW′ isdefined by waveform features of the control logic 90, shown in FIG. 8.These features include positive and negative polarity portions of thewaveform, which are achieved by utilizing the variable polarity switch16 via control lines 55, 56 (discussed above). Similar pulse waves areachieved in other embodiments with voltage or a combination of currentand voltage regulation.

Exemplary pulses 110 of the embodiment shown in FIG. 7 are created bywave shaper 80 at a frequency in the range of 20-400 Hz. For example,this frequency can be selected in an effort to optimize the pulse ratewith the droplet rate of the molten aluminum. The pulse rate contributesto the heat of the weld and the heat in the weld puddle. These twoaspects may be coordinated. Each pulse has a ramp up portion 110 a witha controlled slope, a peak current (I_(PEAK)) 110 b, which is the samefor all pulses shown, a peak time portion 110 c, which is the time thatthe current level is at a peak, a ramp down portion 110 d, a negativecurrent (I_(NEG)) portion for a negative portion time 110 h, and abackground current (I_(BACK)) portion 110 e, which, when not interruptedby a pulse or negative current component, is constant. The ramp up time110 a is included in the peak time 110 g. Although the peak current 110b, peak time 110 g, and the period 110 f remain the same, the amount oftime that the pulse is at the peak current (I_(PEAK)) 110 b is dictatedby the slope of the ramp up portion 110 a. Although not shown in FIG. 7,the shape of the negative polarity components may also include variousslopes associated with the ramp down to the negative current (I_(NEG))and the ramp up from the negative current. In addition, a negativepolarity portion may be introduced anywhere in the pulse wave PW′. Asdiscussed above, the duration of the negative portion 110 h may vary toaccount for variations in power. FIG. 7 shows different negative portiontimes 110 h, 110 h′ to represent the variability of negative portiontimes within the pulse wave PW′.

As shown in FIG. 8, exemplary control logic 90 is provided to create theexemplary pulse wave PW′ of FIG. 7. Control logic 90 may be embodied,for example, as logic, software, or a sub routine, and may utilize adata table to define its operation. For example, as described in moredetail below in association with FIG. 13, workpoints may be establishedfor different specified wire feed speeds WFS, for example, that definefeatures of the pulse wave PW′, which are optimized for that wire feedspeed WFS. Various other features may be used as the basis of anyparticular workpoint. The logic may be embodied in a software program,such as, for example, Lincoln Electric's Weld Development logic program,which is a state-based logic tree specifically for welding. Like otherstate-based programs, the logic may be in a state, running a function,say output current at 300 amps, until a conditional check becomes true(e.g., the peak timer >=2 milliseconds) and then the logic branches tothe next state (defined in the conditional check). These state changescan occur very quickly, stringing together relatively complex logicwithout having to hard program the routine or change a PC board.

In FIG. 8, exemplary logic 90 is defined by steps 124, 126, 128, 129,and 130. The pulse has a ramp up current with a slope that terminates attime tR1, as shown by step 124. Then the peak current portion P1 isimplemented until time tP1, as shown at step 126. Thereafter, there isan exponential decay at a speed 1 until time tS1, as shown by step 128.Then the negative current N1 is implemented until ∫X reaches the desiredenergy level Y, as shown at step 129, where X is the power in watts(I_(a)*V_(a)) during the negative current N1 and Y is the desired energyin joules that correlates to a desired droplet D size. The time when∫X>Y is tN1, i.e., when the negative current N1 ends. Time tN1 may varyfrom cycle to cycle as the time that it takes to reach the desirednegative energy (Y) varies, as discussed above, for example, due tovoltage variations. Background current B1 is maintained until time tB1,as indicated by block or step 130. For example,tB1=t_(PERIOD)−tR1−tP1−tS1−tN1, i.e., the time left over after the otherpulse parameters have been implemented. As mentioned above, thebackground current is maintained constant throughout the welding processembodiment shown in FIG. 7. Although blocks 124, 126, 128, 129, and 130are shown in a particular order to represent the pulse profile or pulsewave PW′ shown in FIG. 7, the features represented by these blocks arenot limited to this sequence or configuration. Many other combinationsof these features may be used to form various pulse wave PW and weldcycle profiles. For example, blocks 129 and 130 may be reversed, suchthat the pulse wave PW created by logic 90 employs the backgroundcurrent B1 before the negative current N1. In addition, other ramp up orramp down features may be integrated into the pulse wave PW, forexample, with the negative current N1.

As discussed above, various calculations may be used to determine whenthe negative polarity portion has resulted in a negative energy level(Y) associated with a desired droplet D size. For example, the integralof voltage may also be used when the current is known. FIG. 9illustrates exemplary logic 300, which may be a sub routine of block129, for example, as shown in FIG. 8, to determine when to end thenegative polarity portion or current N1 based on an integralcalculation. At step 302, the negative polarity portion starts. As shownby step 304, during the negative current N1, the logic 300 calculatesthe integral of a measured parameter X that is indicative of the energycontributing to the size of droplet D. For example, as discussed above,X may be power (specifically discussed in more detail below inassociation with FIG. 10) or voltage during a known current. At step306, the logic 300 compares the integral of X (∫X) to a predetermineddesired energy value Y that corresponds to an amount of energyassociated with a desired droplet D size. If ∫X has not yet reached Y,the logic 300 continues to calculate ∫X in step 304 and compare ∫X to Yin step 306 in a loop until ∫X reaches Y. When ∫X reaches Y, i.e., thedesired energy level associated with the desired droplet D size has beenreached, the logic 300 ends the negative polarity or negative currentN1.

In one embodiment, as discussed above, X is the power in watts(I_(a)*V_(a)) during the negative current N1. FIG. 10 illustratesexemplary logic 400, which may be a sub routine of block 129, forexample, as shown in FIG. 8, to determine when to end the negativepolarity portion or current N1 based on an integral of powercalculation. At step 402, the negative polarity portion starts. At step404, during the negative current N1, the logic 400 measures the voltage(V_(a)), for example, via signal line 54 a shown in FIG. 1. At step 406,the logic 400 measures the current (I_(a)), for example, via signal line52 a shown in FIG. 1. At step 408, the logic 400 calculates power X bymultiplying the current and the voltage (I_(a)*V_(a)). As shown by step410, the logic 400 calculates the integral of power X. At step 412, thelogic 400 compares the integral of power X (∫X) to a predetermineddesired energy value Y that corresponds to an amount of energyassociated with a desired droplet D size. If ∫X has not yet reached Y,the logic 400 continues to measure voltage V_(a), measure current I_(a),calculate power X, and calculate ∫X in steps 404 through 410, andcompare ∫X to Y in step 412 in a loop until ∫X reaches Y. When ∫Xreaches Y, i.e., the desired energy level associated with the desireddroplet D size has been reached, the logic 400 ends the negativepolarity or negative current N1.

A further modification of the invention is illustrated in FIG. 11,wherein a “synergistic” control action is implemented by wave shaper210. The pulses created by this embodiment may be the same as thoseshown in FIG. 7, but may also include other wave forms or cycles. Asmentioned above, the pulses of a cycle include a negative current thatends when a desired energy level is reached. The previously describedcircuitry to obtain this wave shape is schematically represented asblock 212, where 212 can include a look up table with workpointsincluding various WFS parameters (as shown, for example, in FIG. 13, anddescribed in more detail below). As shown in FIG. 11, welder A has thecomponents described in connection with FIG. 1 and includes a wirefeeder 30 so that wire E is fed into the welding operation in accordancewith the level of the WFS signal on line 44. FIG. 11 includes theexemplary motor controller 31, as shown in FIG. 2, but may also utilizeany other suitable motor controller. In addition to the controldescribed in relation to FIG. 1 above, wave shaper 210 controls thesignal on line 44 so it may have different levels associated withdifferent wire feed speeds. Consequently, the modification shown in FIG.11 adds to the previously described embodiment by outputting a voltagelevel on line 44 that tracks the energy level being processed by thewelder A and coordinates the WFS accordingly. In this manner, there is asynergistic effect between the welding energy and the wire feed speedWFS of electrode E.

For example, other embodiments utilizing the concepts employed in thepresent invention are illustrated in FIGS. 12 and 13. In thisembodiment, various parameters, including, for example, wire feed speed(WFS), peak current, peak time, negative current, negative energy, andbackground current, may vary from one workpoint to another. In thisembodiment, as shown in FIG. 12, a synergistic wave shaper 250 isemployed to process a workpoint 254 from look-up table 252 in accordancewith the value of the input signal represented by line 250 a. FIG. 12shows a subset of exemplary workpoints and their associated exemplaryparameters, which may not correspond to the parameter values shown inthe referenced figures. The workpoint represented by the level of thesignal on line 250 a is output in accordance with the look-up table 252.The pulse features and wire feed speed WFS for a selected workpoint areused to control the shape of the pulse by controller 256 and the wirefeed speed by controller 258. For example, the pulse shapes as shown inFIG. 7 may be implemented by the wave shaper or controller 256 by asignal on line 210 a. Coordinated with the power source signal 210 a isa WFS signal on line 44 as directed by controller 258. The wave shaper250 produces a wave shape and a wire feed speed determined by theworkpoint of look-up table 252. The workpoint 254 for the welder isinput to the wave shaper 250 by input line 250 a and output lines 250 b,250 c provide signals to the power source controller 256 and wire feedercontroller 258, respectively.

For example, in one embodiment, a workpoint 254 may generate an outputon line 210 a from the look-up table 252 for pulses having a shape asindicated by pulses 110 in FIG. 7. At the same time, the output on line44 from the look-up table 252 produces a WFS signal corresponding to thepulses 110. The pulses 110 and the wire feed speed WFS are controlledtogether. In accordance with this embodiment, the workpoint from table252 may be changed during each weld cycle, for example, to accommodatevarious welding applications and operating conditions. In otherembodiments, the workpoint parameters may implement other weldingtechniques, such as, for example, shifting between high energy portionsHP and low energy portions LP as described in U.S. Ser. No. 13/788,486.Although the look-up table of FIG. 13 includes current values, otherembodiments may include look-up tables with other parameters, such as,for example, voltage values for embodiments utilizing voltage or acombination of current and voltage regulation.

The embodiments described above may be applied to various other weldingtechniques, such as, for example, short detection and clearing. Inpulsed welding processes, the molten droplet D breaks free of the tip ofthe electrode E and “flies” across the arc toward the workpiece W.However, when the distance between the tip of the electrode E and theworkpiece W is relatively short, the droplet D flying across the arc canmake contact with the workpiece W (i.e., short) while a thin tether ofmolten metal still connects the droplet D to the tip of the electrode E.In such a tethered free-flight transfer scenario, the thin tether ofmolten metal tends to explode, causing spatter, when the droplet D makescontact with the workpiece W, due to a rapid increase in current throughthe tether.

In accordance with an embodiment of the present invention, thecontroller 60 and/or wave shaper 80 may use the sensed voltage signal 52a, the sensed current signal 54 a, or a combination of the two todetermine when a short occurs between the advancing electrode E and theworkpiece W, when a short is about to clear, and/or when the short hasactually cleared, during each pulse period. Such schemes of determiningwhen a short occurs and when the short clears are well known in the art,and are described, for example, in U.S. Pat. No. 7,304,269 and U.S. Ser.No. 13/293,112, which are incorporated herein by reference in theirentirety. The controller 60 and/or wave shaper 80 may modify thewaveform signal when the short occurs and/or when the short is cleared.For example, when a short is determined to have been cleared, thecontroller 60 and/or wave shaper 80 may incorporate a plasma boost pulsein the waveform signal to prevent another short from occurringimmediately after the clearing of the previous short.

FIGS. 14 and 15 show exemplary waveform graphs of pulses that show theincorporation of the embodiments described above with short circuits. Asshown in FIG. 14, an exemplary waveform 500 with an exemplary shortcircuit occurs during or immediately after the exponential decay portion510, but before the onset of a negative polarity portion 520. In thisembodiment, the short circuit is cleared before the negative polarityportion 520 is initiated. After clearing the short circuit, the negativepolarity portion 520 begins. In accordance with the techniques describedin the above embodiments, an integral calculation (e.g., ∫X) is used todetermine when the negative polarity portion 520 has resulted in thedesired energy (e.g., Y) associated with a desired droplet D size. Oncethe desired energy level is reached, the negative polarity portion 520ends at 530. After ending at 530, the exemplary waveform may proceed,for example, to the next pulse peak (as shown in FIG. 14) or to abackground current.

In another embodiment, as shown in FIG. 15, an exemplary waveform 600with an exemplary short circuit occurs after the exponential decayportion 610 and at the onset or during a negative polarity portion 620.In this embodiment, the short circuit is cleared during the negativepolarity portion 620. After clearing the short circuit, the negativepolarity portion 520 continues. If an integral calculation (e.g., ∫X)began before the short circuit, the calculation may restart at 625. Inaccordance with the techniques described in the above embodiments, therestarted integral calculation is used to determine when the negativepolarity portion 620 has resulted in the desired energy (e.g., Y)associated with a desired droplet D size. Once the desired energy levelis reached, the negative polarity portion 620 ends at 630. After endingat 630, the exemplary waveform may proceed, for example, to the nextpulse peak (as shown in FIG. 15) or to a background current.

While the present invention has been illustrated by the description ofembodiments thereof, and while the embodiments have been described insome detail, it is not the intention of the applicant to restrict or inany way limit the scope of the appended claims to such detail.Additional advantages and modifications will readily appear to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details, representative apparatus andmethods, and illustrative examples shown and described. Accordingly,departures may be made from such details without departing from thespirit or scope of the applicant's general inventive concept.

The following is claimed:
 1. An electric arc welder comprising: a highspeed switching power supply configured to create high frequency pulsesthrough a gap between a workpiece and a welding wire advancing towardthe workpiece; a voltage sensor configured to measure a voltage throughthe gap; and a wave shape generator to define a shape of the highfrequency pulses and a polarity of the high frequency pulses, whereinthe wave shape generator is configured to: start a negative polarityportion of a pulse wave, integrate the voltage measured across the gapby the voltage sensor during the negative polarity portion to determinean integrated voltage value during the negative polarity portion,compare the integrated voltage value to a threshold value, and end thenegative polarity portion when the integrated voltage value reaches thethreshold value.
 2. The electric arc welder of claim 1, wherein the waveshape generator is further configured to: determine a power of the pulsewave during the negative polarity portion; integrate the power duringthe negative polarity portion to determine an integrated power valueduring the negative polarity portion; compare the integrated power valueto a second threshold value; and end the negative polarity portion wheneither of the integrated voltage value reaches the threshold value orthe integrated power value reaches the second threshold value.
 3. Theelectric arc welder of claim 2, further comprising a current sensorconfigured to measure a current through the gap, wherein the wave shapegenerator is further configured to: determine the power based on themeasured voltage and the measured current.
 4. The electric arc welder ofclaim 2, wherein the integrated power value is a total energy generatedat the gap during the negative polarity portion.
 5. The electric arcwelder of claim 2, wherein the integrated power value is associated withan energy generated on the welding wire during the negative polarityportion.
 6. The electric arc welder of claim 1, wherein the wave shapegenerator is further configured to: determine a power of the pulse waveduring the negative polarity portion; and compare the power to a secondthreshold value, wherein the second threshold value is associated with awire droplet size.
 7. The electric arc welder of claim 1, wherein afirst duration of a first negative polarity portion of a first pulsecycle is different than a second duration of a second negative polarityportion of a second pulse cycle.
 8. The electric arc welder of claim 1,further comprising a variable polarity switch responsive to the waveshape generator to control the polarity of the high frequency pulses. 9.The electric arc welder of claim 1, further comprising a wire feeder tofeed the welding wire advancing toward the workpiece, wherein the wirefeeder is responsive to the wave shape generator to coordinate a wirefeed speed with the high frequency pulses.
 10. The electric arc welderof claim 2, wherein the negative polarity portion includes a negativecurrent component.
 11. The electric arc welder of claim 2, wherein thenegative polarity portion includes a voltage component.